Men who were circumcised before having sex for the first time (as most circumcised men are) are 15 percent less likely to develop prostate cancer later in life, researchers say. Jose Luis Pelaez, Inc./Blend Images/Corbis

March 13, 2012

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To circumcise or not to circumcise? It's a fraught question for many parents of newborn boys. On one side are religious and cultural traditions favoring the snipping away of a baby's foreskin, and on the other are "intactivists," or anti-circumcision crusaders who consider the practice a form of genital mutilation. Then there are the medical arguments, which are... inconclusive. Adding to the muddle is a new study in the journal Cancer showing that circumcised men have lower rates of prostate cancer, the most common male cancer in the U.S. Here's what you should know:

What exactly did the study show?According to researchers at the University of Washington School of Medicine, men who were circumcised before having sex for the first time are 15 percent less likely to develop prostate cancer and 18 percent less likely to get more aggressive forms of the cancer. The study looked at the medical, family, and sexual histories of 1,754 men with prostate cancer and 1,645 men without it. More than 90 percent of circumcised men said that their procedure was done shortly after birth, long before their first sexual encounter.

What's the link between circumcision and cancer?The researchers aren't entirely sure. Uncircumcised men have been shown to have an increased risk of sexually transmitted infections (STIs), including HIV/AIDS, probably because the foreskin is more likely to tear, and because it creates a moist environment at the tip of the penis that may allow germs to survive for extended periods. One theory posits that STIs inflame the prostate, making it susceptible to the growth of cancer cells. Some 20 percent of cancers worldwide are reportedly caused by infections, directly or indirectly.

Does this mean all boys should be circumcised?No. The study doesn't purport to show a cause-and-effect relationship between circumcision and cancer. "That would be a huge jump," urologist Louis Kavoussi tells WebMD. "There are good reasons to get circumcised, but prostate cancer prevention is not one of them." Some urologists, like Kavoussi, recommend circumcision as a way to reduce STIs and penile cancer. But the evidence for those benefits is weak, and the operation to remove foreskin can cause its own infections. That's why the American Academy of Pediatrics doesn't recommend routine circumcision. The bottom line, says Alexandra Sifferlin at TIME, is that "parents debating whether to circumcise their newborn baby boys still have a difficult decision to make."